I don't know how to spin pens, but I can spin flat surfaces on my index and/or middle fingers. Take a notebook, for example. I'd place my middle finger in the approximate center of it, and use my opposite hand to get momentum for it. As long as you can move your finger in time with the spin object, you can keep it going. I think the longest I've had a book spinning was like 27 minutes. I actually had to switch fingers mid-spin because even though it's light, it puts pressure on your fingers. Took me several weeks to get this technique down.